The MFC Freestyle Pro's are nice fins, i bought one back when I had a Starboard FreeSex. And the fin in my skate is a carbon copy of the MFC freestyle pro, and its pretty sweet for general sailing.
but i'm rubbish at freestyle

, so you can take whatever advice I give with a tub of salt!
I think the pro freestylers will use anything as long as its 16cm or shorter.